1. Field of the Invention
The present invention relates to a focus detecting device adapted for a photographic camera, a video camera and an observation apparatus, or an optical apparatus using the focus detecting device, and more particularly to a focus detecting device arranged to divide the pupil of an objective lens (photographic lens) into a plurality of areas, to obtain a plurality of light distributions relative to an object image by using light fluxes passing through the divided areas and to detect the relative positional relationship of the plurality of light distributions, so that the focusing state of the objective lens can be advantageously detected for a plurality of areas within a photo-taking range.
2. Description of Related Art
Focus detecting devices of a light receiving type called an image-deviation type (phase-difference detecting type) utilizing a light flux passing though an objective lens have been popularly employed as automatic focus detecting devices for photographic cameras, video cameras and the like. Each of these image-deviation type focus detecting devices has optical means arranged on the image-plane side of the objective lens to obtain a plurality of light distributions relative to an object image by using light fluxes passing through the different areas of the pupil of the objective lens. Then, the relative positional relationship of the light distributions is obtained by a photo-electric conversion element composed of a plurality of pixel arrays. The focusing state of the objective lens is thus detected by using signals obtained from the photo-electric conversion element.
Further, some of the focus detecting devices of the image-deviation type area rranged to make a multi-point distance measurement having its distance measuring range cover not only a central area of the viewfinder field, i.e., a photo-taking range, but also some other areas located away from the central area in the vertical or horizontal direction. Each of such multi-point distance measuring focus detecting devices is arranged to have a plurality of focus detecting means, as disclosed, for example, in U.S. Pat. No. 5,005,041.
In the case of such focus detecting devices that are severely required to have a high degree of focusing precision, as in the case of a single-lens reflex camera, an image forming light flux obtained by the objective lens is led to a pair of reimaging lenses. Then, light distributions relative to an object image obtained by the pair of reimaging lenses must be very accurately formed on the pixel arrays of the photo-electric conversion element.
Generally, the arrangement for setting the distance measuring (focus detecting) areas not only in a central area of the photo-taking range but also in other areas located vertically and horizontally away from the central area necessitates use of many focus detecting members. The increase in number of focus detecting members incurs an increase in size of the focus detecting device. Particularly, the increase in size of a sensor chip used for forming the pixel arrays of the photo-electric conversion element causes an increase in cost.
Further, in the arrangement having a plurality of focusing detecting means, images formed on the sensor chip by reimaging lenses include not only images required for focus detection but also as many images as the product of the number of reimaging lenses and the number of focus detecting areas. That arrangement thus results in a drop in focus detecting accuracy caused by unnecessary light or in a further increase in size of the apparatus for eliminating the unnecessary light.